A magnetic pole structure of a motor is, in a linear motor, a structure in which a plurality of magnets having certain length (magnetic pole pitch) are linearly arrayed with polarities thereof set different from one another. In a rotary motor (a brushless motor, etc.), the magnetic pole structure is a structure in which a predetermined number of magnetic poles having polarities different from one another are annularly arrayed to form a predetermined number of poles.
In the linear motor and the rotary motor (the brushless motor, etc.), to detect magnetism in a magnetic pole position where a movable unit is located, two or more magnetic sensors that detect an amount of change corresponding to a distance of a magnetic flux generated by a magnetic pole are arranged at a certain interval along a magnetic pole arraying direction of the motor.
A magnetic pole position detecting device is an apparatus that calculates and detects, based on a phase difference between sensor outputs of two magnetic sensors among the two or more magnetic sensors, the magnetic pole position where the movable unit is located.
In the linear motor, the magnetic pole position detecting device is mounted to obtain position information indicating in which position (magnetic pole position) in a magnetic pole pitch the movable unit is located when the movable unit moves in a magnet arraying direction. Specifically, the magnetic pole position detecting device used in the linear motor includes two magnetic sensors in the device. On the other hand, in the rotary motor, the two or more magnetic sensors form a part of components of the motor. The magnetic pole position detecting device is provided on the outside of the motor.
Concerning an arrangement interval of the two magnetic sensors, in the past, the two magnetic sensors are arranged such that a phase difference between sensor outputs is 90 degrees (e.g., Patent Documents 1 and 2).
Then, in the example of the linear motor, the following relation holds between an arrangement interval L of the two magnetic sensors and a magnetic pole pitch PIT:L=PIT/4  (1)In the rotary motor, the arrangement pitch L is represented by an electrical angle as follows:L=180°/number of poles
Output waveforms of the magnetic sensors are formed in sine wave shapes. Therefore, when the two magnetic sensors are arranged to satisfy the constraint of Formula (1), if a sensor output on an advanced phase side is represented as “a” and a sensor output on a delay phase side is represented as “b”, the sensor output “a” can be regarded as a sine wave and the sensor output “b” can be regarded as a cosine wave. A magnetic pole position can be obtained by calculating a tangent value of the sensor outputs “a” and “b”.
Specifically, if the magnetic pole position is represented as θ, because tan θ=a/b, the magnetic pole position θ can be calculated as follows:θ=tan−1(a/b)  (2)
A processing block in this case, i.e., a magnetic pole position detecting device in the past includes a divider that calculates a/b and a tan−1 angle operator that calculates an arctangent value from the tangent value tan θ calculated by the divider.
Patent Document 1: Japanese Patent Application Laid-open No. S60-180468 (FIG. 3)
Patent Document 2: Japanese Patent Application Laid-open No. 2001-78392 (FIG. 1)